1. Field of the Invention
The invention relates to teleprocessing in general and more particularly to the gathering and transmission of data through a communication channel to a primary processor, of a data processing system, by a plurality of devices which may be remotely located relative to the processor.
2. Prior Art
The rapid development and production of microprocessors have revolutionizedthe way in which multiprocessing systems are configured. Such multiprocessing systems use a plurality of microprocessors for performing the overall data processing functions. Each microprocessor is assigned a dedicated task while at least one of the microprocessors is assigned the task of correlating the results generated from each of the processors.
An electronic point-of-sale terminal is a typical example of a multiprocessing system. In such point of sale terminals a common control processor is assigned the task of processing data received from and to be transmitted to a plurality of terminal devices placed at a plurality of locations. The terminal devices may be remotely located with respect to the control processor. Such terminal devices may include keyboards, alphanumeric displays, operator displays, printers, cash drawers, magnetic card readers, scanners, etc. Each of the devices is provided with a microprocessor which is dedicated to control the device.
Data resulting from transactions carried out at the terminal devices are exchanged between the common control processor and the dedicated device processors. A good many of the transactions require that the data be transmitted and processed on a real time basis. In order to meet the real time requirement, the prior art has adopted several types of system configurations.
One type of prior art system configuration is described in U.S. Pat. No. 4,264,954 Barry D. Briggs et al. The subject patent discribes a distributed function communication system wherein information is exchanged between a host computer and a plurality of remote point of sale terminals. One or more master terminals is placed between the host computer and the remote terminals. Information transmitted from the processor is processed and retained at the master terminals and then serially transmitted to the remote terminals. The effect of the master terminal is transparent to the remote terminals.
U.S. Pat. No. 4,223,380 to Antonaccio et al is another example of the prior art multiprocessing configuration. In the subject patent a common interprocessor bus is used to interconnect a plurality of microprocessor modules. The commonly shared bus serves as a communication path for the microprocessor modules. A communication network routine (CNR) unit is placed in each microprocessor module. The function of the CNR unit is to monitor and control the bus. As a result, the microprocessors are free to perform other functions.
Still other configurations for interconnecting microprocessor modules to form a unified multiprocessing system are given in U.S. Pat. Nos. 4,145,739 (Dunning et al); 4,254,464 (Byrne); 4,394,726 (Kohl) and 4,204,251 (Brudevold).
The Dunning et al patent describes a distributed data processing system for processing informational data. The system consists of a resource memory which stores instruction and informational data. A master central processor is programmed to control the memory. A plurality of slave processor controlled devices are connected via serial communication link (coaxial cables) to the master central processor. Access to the resource memory is under control of the master central processor. Requests by slave devices, for access to the disk or requests to have services performed by another slave device, are stored in dedicated storage areas (called semaphores) of the requesting slave devices. The areas are periodically polled and read by the master. Once the master completes the requested services, the master resets the storage area to a value indicating that the requested service has been completed.
The Byrne patent describes the use of a common data buffer for interfacing a plurality of minicomputers with a space vehicle. Each of the minicomputers communicates with the buffer through buffer access cards. A high speed scanner is connected to each of the buffer access cards. The scanner is provided for transferring the information stored in the buffer access card in a predetermined sequence to and from the common data buffer memory.
The Kohl patent describes a multiport memory access architecture for a bus communication network. Devices which are connected to the bus are granted direct memory access (DMA) privilege in a predetermined sequence with selected devices being given access more than once in the sequence. Each device must raise a "request signal" to gain entry into the storage.
Finally, the Brudevold patent describes an interface for interconnecting multiple data processors in a distributed data processing network. The interface is used to transfer data between the processors. In order to use the interface, a processor must generate a message requesting its use.